1. Field of the Invention
This invention relates to an image communication system, an image server, a method of controlling operation of the image server and a medium storing a computer program for controlling the operation of the image server.
2. Description of the Related Art
It is possible to communicate with an image server and display an image, which is represented by image data transmitted from the image server, on the display screen of a mobile telephone. If the image is large, the image is reduced in size so as to fit the size of the display screen because the display screen of a mobile telephone is comparatively small. When the image is reduced in size, the displayed image becomes difficult to view. In order to deal with this, there is a technique whereby part of the image is displayed on the display screen and the remainder of the image is displayed based upon image data transmitted from the image server to the mobile telephone in accordance with a scrolling operation performed by the user (see the specification of Japanese Patent Application Laid-Open No. 2009-86482). Usually, however, the image data transmitted from the image server to the mobile telephone is image data that has been compressed. In general, this compression is based upon the JPEG (Joint Photographic Experts Group) scheme (see the specification of Japanese Patent Application Laid-Open No. 2001-86318). With JPEG-based compression, image data is compressed in a prescribed order block by block, where each block is composed of a plurality of pixels, and the image data is expanded in the prescribed order. Depending upon the scrolling direction, the order of the remaining image portions displayed and the scrolling direction may not coincide owing to expansion. Even if scrolling is performed, therefore, locations where no image exists arise and viewing becomes difficult.